A permanent magnet brush motor usually comprises a stator and a rotor. The stator comprises a housing and permanent magnets mounted to the inner surface of the housing. The rotor comprises a rotation shaft, a magnetic core and a commutator fixed to the rotation shaft, and a rotor winding wound around the magnetic core. There exists the tooth-slot effect between the stator and the rotor. In some applications, it is expected that the motor has a larger cogging torque. For example, for roller shutter motors, it is desirable to increase the cogging torque of motor so that the motor can stop the shutter at any designated positions without additional brake devices to thereby simplify the structure and reduce the cost of the roller shutter.
A traditional outer rotor brushless DC motor is provided with a base at one end of the motor, a mounting post protrudes axially in the middle of the base and is configured for supporting the stator of the motor. The mounting post is hollow inside for the motor shaft axially passing therethrough. Two bearing housings is mounted to in the mounting post to rotatably support the motor shaft. The mounting post should be greater enough for accommodating the bearings. However, the increasing size of the mounting post will increases the difficulty of integrally forming the mounting post with the base, and leads to the increase of the radial size of the stator core. In addition, since the bearings are both mounted in the mounting post, the mounting post must be made with high strength materials to make the mounting post can completely support the rotor and a load, such as an impeller, carried by the rotor. In addition, to ensure high concentricity between the bearings disposed in the bearing seat, it is necessary to finish the mounting post. All the points aforementioned will lead to increased manufacture cost of an outer rotor motor.